Things to try-
we all have various causes & factors so it may or may not help , but might be worth gently testing these.
* slow & easy works better than going all out and then backwards.. due to the delayed pain factor*
Sharon Butler's website explains why gentle stretching is better than hard core forcing stretches.. I found the info very helpful.
Repetitive Strain Injury Self Care

https://www.neurotalk.org/members/100-albums422.html
I spent a lot of time on a soft rolled up towel then got a foam roller & large exercise ball - they all worked for me..

Trigger point work- we have a sticky thread about it..
Top rib mobilization - was a big plus for me --a forum search or web search will find info on it

My version of TOS was due to work postures 15 yrs, past whiplash, past shoulder injuries, plus hyper mobility.. mainly soft tissue based.